Knowing your aquarium's exact water volume matters for stocking decisions, medication dosing, and filter sizing, and a tank's advertised "gallon" size is often rounded rather than the precise mathematical volume of its dimensions.
This calculator takes your tank's internal length, width, and height in inches and calculates the exact volume in both US gallons and liters using the standard cubic-inch-to-gallon conversion.
Because glass thickness slightly reduces the actual interior water volume compared to the tank's external dimensions, measuring the interior dimensions (rather than the outside of the glass) gives a more accurate result, especially for larger or thicker-glass tanks.
Because everything runs locally in your browser, results appear instantly and nothing you type or upload is ever sent to a server.
Bookmark this page if you expect to use this tool regularly — it loads fast and behaves the same way every time, with no account needed.
This kind of task shows up constantly in everyday writing, coding, design, and admin work, which is exactly why a dedicated, focused tool saves so much back-and-forth.
A tool that does one job well, without a cluttered interface or unrelated features competing for attention, tends to be faster to use than a heavier all-in-one app.
If you find yourself needing this often, keeping this page open in a tab is usually faster than digging through a bigger software suite's menus.
Because there's no sign-up or installation step, you can jump straight from a search result to a working tool in a couple of seconds.
The interface is intentionally simple, so there's no learning curve — the input goes in, the result comes out, and that's the whole interaction.
Unlike a heavier desktop application, there's nothing to download, update, or configure before you can start using this tool.
Frequently asked questions
Should I measure the inside or outside of the glass?
For the most accurate water volume, measure the interior dimensions; using exterior dimensions will overestimate the true water capacity, especially noticeably on tanks with thick glass.
Why doesn't my tank hold its full calculated volume of water?
Substrate, decorations, and the water line typically sitting an inch or so below the rim all reduce the actual water volume below the tank's full mathematical capacity.